The present invention is directed toward methods and apparatuses for shaping and/or orienting radiation directed toward a microlithographic substrate. Microelectronic features are typically formed in microelectronic substrates (such as semiconductor wafers) by selectively removing material from the wafer and filling in the resulting openings with insulative, semiconductive, or conductive materials. One typical process includes depositing a layer of radiation-sensitive photoresist material on the wafer, then positioning a patterned mask or reticle over the photoresist layer, and then exposing the masked photoresist layer to a selected radiation. The wafer is then exposed to a developer, such as an aqueous base or a solvent. In one case, the photoresist layer is initially generally soluble in the developer, and the portions of the photoresist layer exposed to the radiation through patterned openings in the mask change from being generally soluble to become generally resistant to the developer (e.g., so as to have low solubility). Alternatively, the photoresist layer can be initially generally insoluble in the developer, and the portions of the photoresist layer exposed to the radiation through the openings in the mask become more soluble. In either case, the portions of the photoresist layer that are resistant to the developer remain on the wafer, and the rest of the photoresist layer is removed by the developer to expose the wafer material below.
The wafer is then subjected to etching or ion implantation processes. In an etching process, the etchant removes exposed material, but not material protected beneath the remaining portions of the photoresist layer. Accordingly, the etchant creates a pattern of openings (such as grooves, channels, or holes) in the wafer material or in materials deposited on the wafer. These openings can be filled with insulative, conductive, or semiconductive materials to build layers of microelectronic features on the wafer. The wafer is then singulated to form individual chips, which can be incorporated into a wide variety of electronic products, such as computers and other consumer or industrial electronic devices.
When the photoresist layer is exposed to radiation, the radiation passing through the apertures of the mask or reticle diffracts to form a diffraction pattern that is collected by an optic system and projected onto the photoresist layer. The imaged or projected diffraction pattern defines the features formed in the photoresist layer. Accordingly, the radiation can form a central or zeroth diffraction order, a first diffraction order positioned outwardly on each side of the zeroth order, and possibly second or higher diffraction orders disposed outwardly from the first orders. The smaller the aperture in the reticle, the greater the angle between the zeroth diffraction order and the first diffraction order. If the aperture is reduced in size (for example, to reduce the size of the features in the wafer), the first diffraction order may spread out so far from the zeroth order that it is no longer captured by the optic system and projected onto the photoresist layer. This can adversely affect the quality of image formed on the photoresist layer because the first diffraction order is generally required to adequately define the image projected onto the photoresist layer.
One approach to addressing the foregoing problem is to direct the radiation beam incident on the reticle aperture at an angle relative to the optical axis using a series of optical elements positioned between the radiation source and the reticle. For example, the optical elements (optionally in conjunction with a blade) can form a radiation beam that initially has an annular cross-sectional shape and is directed generally parallel to the optical axis. The radiation beam then passes through a series of optical elements that direct the radiation at an angle to the optical axis. Accordingly, the radiation incident on the reticle aperture will pass through the aperture at an angle. This can effectively tilt the diffraction pattern. As a result, this method can improve the likelihood for capturing one of the first diffraction orders, possibly at the expense of the other.
One drawback with the foregoing approach is that the lenses that shape the radiation beam can have aberrations that adversely affect the quality of the images they produce. One general approach to correcting lens aberrations in wafer optic systems (disclosed in U.S. Pat. No. 5,142,132 to McDonald et al.), is to reflect the radiation beam from a deformable mirror, which can be adjusted to correct for the aberrations in the lens optics.
However, another drawback with the beam-shaping lens system is that it is relatively inflexible. Accordingly, it is difficult to adequately tailor the beam shape (and therefore the resulting incidence angle of the radiation) to different reticle apertures or aperture patterns because the number of available beam shapes for a given optics system may be limited, and it may be time consuming to change one optics system or system set-up for another.
The present invention is directed to methods and apparatuses for shaping radiation directed to a microlithographic substrate. In one aspect of the invention, the method can include directing a beam of radiation along a radiation path toward a reflective medium, with the beam having a first shape in a plane generally transverse to the radiation path. The method can further include changing a shape of the radiation beam from the first shape to a second shape different than the first shape by inclining a first portion of the reflective medium relative to a second portion of the reflective medium, and reflecting the beam from the reflective medium toward a microlithographic substrate. The method can still further include impinging the beam on the microlithographic substrate after changing the shape from the first shape to the second shape.
In a further aspect of the invention, the radiation beam can have a first intensity prior to impinging on the reflective medium and the method can further include directing the radiation beam away from the reflective medium with the second shape and with a second intensity at least approximately the same as the first intensity. The method can still further include changing an angle of at least a portion of the radiation relative to the radiation path by impinging the radiation beam on an optical element after changing the shape of the beam from the first shape to the second shape.
The invention is also directed toward an apparatus for irradiating a radiation-sensitive surface of a microlithographic substrate. The apparatus can include a support member configured to releasably support the microlithographic substrate, and a radiation source configured to emit a beam of radiation along a radiation path directed toward the support member. A reticle is positioned along the radiation path and is configured to pass the radiation toward the substrate support. A reflective medium is also positioned along the radiation path and has a first portion and a second portion with the first portion movable relative to the second portion to change a shape of the radiation beam in a plane generally transverse to the radiation path from a first shape to a second shape different than the first shape. An optical element can be positioned between the reflective medium and the support member to receive radiation from the reflective medium and direct at least some of the radiation at an angle relative to the radiation path. A controller can be operatively coupled to the reflective medium and can be configured to direct the first portion of the reflective medium to move relative to the second portion to change the shape of the radiation beam from the first shape to the second shape.